The present invention relates to a recording medium cartridge housing, for example, an optical disk or a magneto-optical disk as a recording medium enabling recording/reproduction of information such as audio signals, image signals and the like, and relates more specifically to a recording medium cartridge comprising a printed layer which enables writing on the main surface of the cartridge body.
Currently, recording media for recording/reproducing music and images are widely prevalent in general. Of these media, a small disk cartridge referred to as a MiniDisc™ (MD) is widely used not only indoors but outdoors as well as in vehicles. This disk cartridge is made, as shown in FIG. 6, by rotatably housing an optical disk or a magneto-optical disk 4 inside a cartridge body 3 made by assembling an upper half 1 and a lower half 2 through ultrasonic welding. When not in use, a shutter 5 blocks an opening in the cartridge body 3, and adhesion of foreign material to the disk 4 is thus prevented.
Ordinarily, titles of the songs recorded on the disk cartridge are written on a label sticker to be stuck on a main surface 3a of the cartridge body 3. However, there is a possibility that the sticker would come off as the adhesiveness deteriorates due to changes over time, and as a result that the disk cartridge may become unejectable from a recording/reproducing apparatus (deck).
In order to solve this, there are products in which a printed layer 8, which makes writing possible, is provided on the main surface 3a of the cartridge body 3 instead of the label sticker mentioned above. The conventional printed layer 8 comprises an ink 7 containing a writing-enabling filler 6, such as calcium carbonate, silica, protein powder, which makes writing possible. The filler 6 forms appropriate bumps and dents on the surface of the printed layer 8, and thus achieves writability. Also, since the filler 6 has water absorbing properties, writing with water-based ink is made possible.
However, because the printed layer 8 containing the filler 6 is vulnerable to rubbing and friction, there is a problem in that it brings about a drop in aesthetic quality as the printed layer 8 is grazed and marred due to pressure welding between a welding horn 9 and the upper half 1 as shown in FIG. 8 at the time of ultrasonic welding of the upper and lower halves 1 and 2 in a step for manufacturing the disk cartridge. In other words, there is a problem in that by being subjected to ultrasonic vibration in a state where the writing-enabling filler 6 in the printed layer 8 and the welding horn 9 are in contact, the filler 6 falls out from the ink 7 or changes shape, thereby bringing about a drop in the aesthetic quality of the printed layer 8 and ultimately of the disk cartridge.
The present invention is proposed in view of the problems mentioned above, and makes it its issue to provide a recording medium cartridge capable of preventing a drop in aesthetic quality by preventing damage to the printed layer for writing during ultrasonic welding.